16x2 Lcd display with Raspberry pi using I2C

 import smbus  
 from time import *  
 class i2c_device:  
   def __init__(self, addr, port=1):  
    self.addr = addr  
    self.bus = smbus.SMBus(port)  
 # Write a single command  
   def write_cmd(self, cmd):  
    self.bus.write_byte(self.addr, cmd)  
    sleep(0.0001)  
 # Write a command and argument  
   def write_cmd_arg(self, cmd, data):  
    self.bus.write_byte_data(self.addr, cmd, data)  
    sleep(0.0001)  
 # Write a block of data  
   def write_block_data(self, cmd, data):  
    self.bus.write_block_data(self.addr, cmd, data)  
    sleep(0.0001)  
 # Read a single byte  
   def read(self):  
    return self.bus.read_byte(self.addr)  
 # Read  
   def read_data(self, cmd):  
    return self.bus.read_byte_data(self.addr, cmd)  
 # Read a block of data  
   def read_block_data(self, cmd):  
    return self.bus.read_block_data(self.addr, cmd)  
 # LCD Address  
 ADDRESS = 0x27  
 # commands  
 LCD_CLEARDISPLAY = 0x01  
 LCD_RETURNHOME = 0x02  
 LCD_ENTRYMODESET = 0x04  
 LCD_DISPLAYCONTROL = 0x08  
 LCD_CURSORSHIFT = 0x10  
 LCD_FUNCTIONSET = 0x20  
 LCD_SETCGRAMADDR = 0x40  
 LCD_SETDDRAMADDR = 0x80  
 # flags for display entry mode  
 LCD_ENTRYRIGHT = 0x00  
 LCD_ENTRYLEFT = 0x02  
 LCD_ENTRYSHIFTINCREMENT = 0x01  
 LCD_ENTRYSHIFTDECREMENT = 0x00  
 # flags for display on/off control  
 LCD_DISPLAYON = 0x04  
 LCD_DISPLAYOFF = 0x00  
 LCD_CURSORON = 0x02  
 LCD_CURSOROFF = 0x00  
 LCD_BLINKON = 0x01  
 LCD_BLINKOFF = 0x00  
 # flags for display/cursor shift  
 LCD_DISPLAYMOVE = 0x08  
 LCD_CURSORMOVE = 0x00  
 LCD_MOVERIGHT = 0x04  
 LCD_MOVELEFT = 0x00  
 # flags for function set  
 LCD_8BITMODE = 0x10  
 LCD_4BITMODE = 0x00  
 LCD_2LINE = 0x08  
 LCD_1LINE = 0x00  
 LCD_5x10DOTS = 0x04  
 LCD_5x8DOTS = 0x00  
 # flags for backlight control  
 LCD_BACKLIGHT = 0x08  
 LCD_NOBACKLIGHT = 0x00  
 En = 0b00000100 # Enable bit  
 Rw = 0b00000010 # Read/Write bit  
 Rs = 0b00000001 # Register select bit  
 class lcd:  
   #initializes objects and lcd  
   def __init__(self):  
    self.lcd_device = i2c_device(0x3f)  # I2C module LCD Address
    self.lcd_write(0x03)  
    self.lcd_write(0x03)  
    self.lcd_write(0x03)  
    self.lcd_write(0x02)  
    self.lcd_write(LCD_FUNCTIONSET | LCD_2LINE | LCD_5x8DOTS | LCD_4BITMODE)  
    self.lcd_write(LCD_DISPLAYCONTROL | LCD_DISPLAYON)  
    self.lcd_write(LCD_CLEARDISPLAY)  
    self.lcd_write(LCD_ENTRYMODESET | LCD_ENTRYLEFT)  
    sleep(0.2)  
   # clocks EN to latch command  
   def lcd_strobe(self, data):  
    self.lcd_device.write_cmd(data | En | LCD_BACKLIGHT)  
    sleep(.0005)  
    self.lcd_device.write_cmd(((data & ~En) | LCD_BACKLIGHT))  
    sleep(.0001)  
   def lcd_write_four_bits(self, data):  
    self.lcd_device.write_cmd(data | LCD_BACKLIGHT)  
    self.lcd_strobe(data)  
   # write a command to lcd  
   def lcd_write(self, cmd, mode=0):  
    self.lcd_write_four_bits(mode | (cmd & 0xF0))  
    self.lcd_write_four_bits(mode | ((cmd << 4) & 0xF0))  
   # write a character to lcd (or character rom) 0x09: backlight | RS=DR<  
   # works!  
   def lcd_write_char(self, charvalue, mode=1):  
    self.lcd_write_four_bits(mode | (charvalue & 0xF0))  
    self.lcd_write_four_bits(mode | ((charvalue << 4) & 0xF0))  
   # put string function  
   def display_line(self, string, line):  
    if line == 1:  
      self.lcd_write(0x80)  
    if line == 2:  
      self.lcd_write(0xC0)  
    if line == 3:  
      self.lcd_write(0x94)  
    if line == 4:  
      self.lcd_write(0xD4)  
    for char in string:  
      self.lcd_write(ord(char), Rs)  
   # clear lcd and set to home  
   def clear(self):  
    self.lcd_write(LCD_CLEARDISPLAY)  
    self.lcd_write(LCD_RETURNHOME)  
   # define backlight on/off (lcd.backlight(1); off= lcd.backlight(0)  
   def backlight(self, state): # for state, 1 = on, 0 = off  
    if state == 1:  
      self.lcd_device.write_cmd(LCD_BACKLIGHT)  
    elif state == 0:  
      self.lcd_device.write_cmd(LCD_NOBACKLIGHT)  
   # add custom characters (0 - 7)  
   def lcd_load_custom_chars(self, fontdata):  
    self.lcd_write(0x40);  
    for char in fontdata:  
      for line in char:  
       self.lcd_write_char(line)       
   # define precise positioning (addition from the forum)  
   def display(self, string, line, pos):  
   if line == 1:  
    pos_new = pos  
   elif line == 2:  
    pos_new = 0x40 + pos  
   elif line == 3:  
    pos_new = 0x14 + pos  
   elif line == 4:  
    pos_new = 0x54 + pos  
   self.lcd_write(0x80 + pos_new)  
   for char in string:  
    self.lcd_write(ord(char), Rs)